Variable microwave phase shifter utilizing plasma electrode



Feb. 15, 1966 H. MAGNUSKI 3,

VARIABLE MICROWAVE PHASE SHIFTER UTILIZING PLASMA ELECTRODE Filed April 16, 1965 I J0 w FIG] l I \I 3 A AMPL|FIER& fag I I mmmuu. B l l5 ATTLZIFIER /3'\ D ljx l FREQMULT.

PHASE SHIFT J D CONTROL LEADS TO PHASE SHIFT CONTROL INVENTOR HENRY MAGNUSKI 5 6 ATTYS.

United States Patent Gfl ice 3,235,768 Patented Feb. 15, 1966 3,235,768 VARIABLE MICROWAVE PHASE SHIFTER UTILIZING PLASMA ELECTRODE Henry Magnuski, Glenview, lll., assignor to Motorola, Inc., Franklin Park, 111., a corporation of Illinois Filed Apr. 16, 1963, Ser. No. 273,332 6 Claims. (Cl. 31539) This invention relates to microwave apparatus, and more particularly to a device for shifting the phase of microwaves in a waveguide.

Various devices have been proposed for variably shifting the phase of microwaves being transmitted in a waveguide. Some of these devices operate by mechanically varying the dimensions of the waveguide through a servo mechanism or similar arrangement. Another possible way of shifting phase is to utilize ferrite material of various configurations which are magnetized by an electromagnet connected to a control system.

The difiiculties with such presently known systems are numerous. Electromagnet coils or servo motors require considerable power, making remote control of such systems diflieult and complicated. In addition, the phase shifters are often excessively expensive due to the elaborate apparatus that must be used to operate them. Finally, the inherent delay in such mechanical or electromagnetic devices makes very rapid phase shifting virtually impossible.

One application in which very rapid phase shifting is desirable is in electronically steering directional antennas, often referred to as phased antenna arrays. The phase relationship of the various microwave input signals in a phased antenna array determines the direction of the beam, an in order to shift this direction rapidly and without complex machinery, electronic phase shifting is extremely desirable.

Accordingly, it is an object of this invention to provide an electronic microwave phase shifter capable of very rapidly shifting the phase of microwaves traveling therethrough.

Another object of the invention is to provide an improved microwave phase shifter which is simple of construction and low in cost.

A further object of the invention is to provide a microwave phase shifter which provides phase shift up to 360 with minimum power requirements.

A further object of the invention is to provide an electronic on-off switch for a waveguide.

A feature of the invention is the provision of a waveguide filled with an ionizable transmitting medium, and having an electrode therein which ionizes variable portions of the medium to effectively vary the dimensions of the waveguide and thereby vary the phase of microwaves passing therethrough.

Another feature of the invention is the provision of a sealed waveguide section filled with a transmitting medium which may be ionized with electrodes therein providing an increasing gap therebetween according to the distance from the wall of the waveguide, and the further provision of means impressing a varying voltage of the waveguide and the electrode to effectively raise and lower the bottom of the waveguide by ionizing varying amounts of the transmitting medium sufiiciently to cause the same to reflect the waves.

In the drawing:

FIG. 1 is a schematic diagram of a phased antenna array radar system incorporating the invention;

FIG. 2 is a schematic diagram illustrating microwave propagation characteristics in waveguides;

FIG. 3 is a side elevation of a microwave phase shifter constructed in accordance with the invention; and

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

In practicing the invention, a section of the waveguide is filled with an ionizable transmitting medium such as an inert gas. An electrode arrangement is placed in the waveguide to ionize portions of the transmitting medium a degree sufficient to cause the same to reflect the waves according to an energizing voltage applied to the electrodes. The electrodes are so placed that the ionized gas efi'ectively changes the dimensions of the waveguide by reflecting the microwaves. One suitable construction includes a wedge-shaped electrode extending from the bottom of a gas filled waveguide of rectangular cross-section. A potential applied between the electrode and the sides of the waveguide ionizes the gas therebetween in varying amounts according to its strength sufliciently to cause the same to reflect the waves, effectively raising the bottom of the waveguide according to the size of the potential applied across the electrode and the sides. This changes the wavelength of microwaves passing through the waveguide and when they leave the waveguide their phase is shifted accordingly.

Referring now to FIG. 1, an example of an electronically steered antenna system, or phased antenna array, is depicted schematically. An electronically steered antenna system may consist of hundreds or thousands of dipole antennas attached to a flat supporting structure 10 which is usually immobile. The phase of the radio frequency energy feeding each dipole is so controlled that the total radiation from the structure is in the form of a narrow beam which may be directed as desired. In the example of FIG. 1, only 3 aligned dipoles 11, 13, and 15 are shown for purpose of illustration. For transmitting purposes these dipoles 11, 13 and 15 are fed by separate low power RF amplifier-multipliers 17, 19 and 21. The RF amplifier-multiplier units may be excited from a single master oscillator-modulator 23 through a waveguide network 25, which includes controlled phase shifters 27, 29, and 31.

If the same phase is fed to all dipoles, the radiation beam will be perpendicular to the dipole plane. This is illustrated by beam A. However, if for example, the phase is shifted forward in dipole 11 and backward by the same amount in dipole 15, the beam will be directed downwards as shown by B. The plane of wavefronts corresponding to the beams A and B, is shifted through the angle theta defined by lines C and D respectively. For relatively small values, 0 may be approximated according to the equation Sin TE propagation mode, the wavelength k in the waveguide can be calculated from the following well-known equation x 2 v (all then 3 2 k =3 1( =.75 om.

Let us take a section of the waveguide 31 long or 3 -3.75 cm.=1l.25 cm. long (approximately 4 /2"). This is shown in the top portion of FIG. 2. If dimension h is changed from 2.5 cm. to 1.77 cm. (from 1" to approximately 0.7") the new dimension 11 will cause k to increase to x '=5.625 cm. As may be seen from the lower portion of FIG. 2, only two full wavelengths will fit in the same length of waveguide where three full wavelengths were previously available. Thus by changing the dimension h from 2.5 cm, to 1.77 cm., a continuous phase shift of 360 in the wave traveling through this section of waveguide may be obtained.

Referring now to FIGS. 3 and 4, the detailed construction of one of the phase shifters 27 is illustrated. A piece of a waveguide 35 is equiped with window seals 37 at each end. Seals 37 contain flanged portions 39 thereon for connection in the waveguide network. Waveguide section 35 is filled with some type of ionizable transmitting medium such as an inert gas or mixture of gases under appropriate pressure. One short wall 35a of waveguide section 35 has an elongated slot formed therein to accommodate an ionizing electrode 41. The opening through which electrode 41 protrudes is formed by a pair of flanged portions 43 in the short wall 35a of waveguide section 35. The electrode 4 1 is insulated from waveguide section 35 by appropriate isolating and sealing material 45, such as ceramic or glass. The length of protruding wall 43 may be so selected that, depending on the dielectric constant of insulator d5, it constitutes a quarter wavelength choke to prevent electromagnetic energy from escaping from the waveguide through the slot for electrode 41.

If electrode 41 has no voltage applied to it, the gas filling waveguide section 35 will not be ionized and the dimension of the waveguide which determines the wavelength will be approximately the full dimension of the waveguide, h as shown in FIG. 4. However, if appropriate ionizing voltage and current is applied between the electrode 41 and the body of waveguide section 35, partial ionization of the gas will take place. Because of the wedge shape of the electrode 41, the gas will first be ionized in the space where the distance from electrode 41 to the wall of waveguide section 35 is the shortest. This space is indicated by the dotted lines in FIG. 4.

It is well known (for example see paper entitled Microwave Applications, by Frank R. Arams, Electronics Magazine, November 1954, pages 168l72) that if a gas is sufficiently ionized to have a negative dielectric constant, the gas acts to reflect the microwaves in the same way as a conductive sheet or wall. Accordingly, to the microwave energy traveling in the waveguide, the limit of the space which is sufliciently ionized to reflect the waves will correspond to a new dimension of the waveguide h shown in FIG. 4, and to a different wavelength in this waveguide. If the ionizing voltage and current is increased, the reflective ionization will occupy more and more space until it reaches the top of ionizing electrode 41. Therefore, in effect the conductive wall of the waveguide can be shifted in accordance with the applied ionizing voltage and current. By controlling the ionizing voltage and current applied to a section of such a waveguide, it is possible to remotely control the waveguides larger dimension and thus, the wavelength and phase of the energy passing through such Waveguide. Relatively small power will be required tor such a phase control if the transmitting medium is carefully selected. For example, in the case of an inert gas, the mixture and pressure thereof would have to be properly selected. Almost no delay will be experienced because it takes a fraction of a microsecond to ionize the transmitting medium.

It is further possible in accordance with the invention, to select such a dimension of the ionizing electrode 41 that the dimension [1' may be made smaller than M2 upon application of sutficient voltage. When this occurs, it will be seen from the equation that the Wavelength A becomes infinitely long and the waveguide does not support propagation. Accordingly, the waveguide effectively becomes an open switch.

It may therefore be seen that the invention provides an improved low cost microwave phase shifter which requires a minimum of power for a 360 phase shift. The invention further provides rapid control of the phase shift by electronically changing the larger dimension of the waveguide section through which microwaves are traveling. Moreover, the invention may be utilized as an electronic waveguide switch to completely block the passage of microwaves.

I claim:

1. A microwave phase shifter including in combination, waveguide means having a pair of oppositely disposed shorter sides and a pair of oppositely disposed longer sides, said waveguide means further having a fluid confining window at either end which permits passage of microwaves therethrough and containing ionizable fluid occupying the interior, said ionizable fluid having the property of passing microwaves when not ionized to a given degree and of reflecting the same when ionized to the given degree, ionizing electrode means in said waveguide means, said electrode means extending along a given length of said waveguide means and protruding from a shorter side thereof a given distance, and energizing means connected to said electrode means for causing the same to ionize that portion of said fluid occupying the space in said waveguide means between said electrode means and said longer sides to the given degree, such ionization of said fluid thereby serving to effectively reduce the size of said waveguide means, whereby the phase of microwaves in said waveguide means is correspondingly changed.

2. A microwave phase shifter including in combination, waveguide means having a pair of oppositely disposed shorter sides and. a pair of oppositely dispose-d longer sides, said waveguide means further having a gas confining window at either end which permits passage of microwaves therethrough, an ionizable gas occupying the interior of said waveguide means and having the property of passing microwaves when not ionized to a given degree and of reflecting the same when ionized to the given degree, ionizing electrode means in said waveguide means, said electrode means having a portion extending along a given length of said waveguide means and protruding from a shorter side thereof a given distance, said electrode means being of a configuration such that the ionizing gap therein increases with the distance said portion protrudes from the shorter side of said waveguide means, and variable energizing means connected to said electrode means for causing the same to ionize variable portions of said gas occupying the space in said waveguide means between said portion of said electrode means and said longer sides to the given degree, such ionization of said gas thereby serving to eflectively vary the greater dimension of said waveguide means so that the phase of the microwaves in the said waveguide means is correspondingly varied.

3. A microwave phase shifter including in combination, a waveguide of rectangular cross-section and having a gas confining window at either end which permits the passage of microwaves therethrough, an ionizable gas occupying the interior of said waveguide and having the property of passing microwaves when not ionized to a given degree and of reflecting the same when ionized to the given degree, a wedge shaped ionizing electrode protruding from one side of said waveguide into the interior thereof and extending along a given length of said wave guide, and variable energizing means impressing a voltage across said electrode and the sides of said waveguide adjacent said one side for causing the same to sufiiciently ionize variable portions of said gas occupying the space between said electrode and the sides adjacent said one side to reflect microwaves, such ionization of said gas thereby serving to eflectively vary the larger cross-sectional dimension of said waveguide so that the phase of microwaves in said waveguide is correspondingly varied.

4. A microwave phase shifter including in combination, a waveguide having a top, bottom and two sides forming a rectangular cross-section, first and second gas confining windows at respective ends of said waveguide which permits passage of mircowaves therethrough, an ionizable gas occupying the interior of said waveguide and having the property of passing microwaves when not ionized to a given degree and of reflecting the same when ionized to the given degree, a wedge shaped ionizing electrode protruding into the interior of said waveguide from the bottom thereof and extending substantially along the entire length of said bottom, and variable energizing means connected to said electrode and said sides of said waveguide for impressing a voltage .thereacross to sufliciently ionize variable portions of said gas occupying the space between said electrode and said sides to reflect microwaves, such ionization of said gas thereby serving to effectively vary the height of said waveguide, whereby the phase of microwaves in said waveguide is correspondingly varied.

5. A microwave phase shifter including in combination, a waveguide having a top, bottom and two sides forming a rectangular cross-section, first and second gas confining windows at respective ends of said waveguide which permits passage of microwaves therethrough, an ionizable gas occupying the interior of said waveguide and having the property of passing microwaves when not ionized to a given degree and of reflecting the same when ionized to the given degree, a wedge shaped ionizing electrode protruding into the interior of said waveguide from the bottom thereof and extending substantially along the entire length of said bottom, and variable energizing means connected to said elctrode and said sides of said waveguide for impressing a voltage thereacross to sufliciently ionize variable portions of said gas occupying the space between said electrode and said sides to reflect microwaves, such ionization of said gas thereby serving to effectively vary the height of said waveguide, said electrode protruding into said waveguide a distance suflicient to enable ionization of said gas to an extent which reduces the effective height of said waveguide to not more than half the wavelength of the microwaves in said waveguide whereby said microwaves may be cut off.

6. A microwave phase shifter including in combination, waveguide means having a pair of oppositely disposed shorter sides and a pair of oppositely disposed longer sides, said waveguide means further having a gas confining window at either end which permits passage of microwaves therethrough, an ionizable gas occupying the interior of said waveguide means, ionizing electrode means in said waveguide means, said electrode means having a portion extending along a given length of said waveguide means and protruding from a shorter side thereof a given distance, said electrode means being of a configuration such that the ionizing gap therein increases with the distance said portion protrudes from the shorter side of said waveguide means, and variable energizing means connected to said electrode means for causing the same to sufliciently ionize variable portions of said gas occupying the space in said waveguide means between said portion of said electrode means and said larger sides to reflect microwaves, such ionization of said gas thereby serving to effectively vary the greater dimension of said waveguide means, said given distance being suflicient to enable ionization of said gas to an extent which reduces the effective greater dimension of said waveguide to not more than half the wavelength of the microwaves in said waveguide, whereby said microwaves may be cut off.

References Cited by the Examiner UNITED STATES PATENTS 1/1962 Brown et al 343-771 4/1963 Fisch 343-895 OTHER REFERENCES HERMAN KARL SAALBACH, Primary Examiner. 

1. A MICROWAVE PHASE SHIFTER INCLUDING IN COMBINATION, WAVEGUIDE MEANS HAVING A PAIR OF OPPOSITELY DISPOSED SHORTER SIDES AND A PAIR OF OPPOSITELY DISPOSED LONGER SIDES, SAID WAVEGUIDE MEANS FURTHER HAVING A FLUID CONFINING A WINDOW AT EITHER END WHICH PERMITS PASSAGE OF MICROWAVES THERETHROUGH AND CONTAINING IONIZABLE FLUID OCCUPYING THE INTERIOR, SAID IONIZABLE FLUID HAVING THE PROPERTY OF PASSING MICROWAVES WHEN NOT IONIZED TO GIVEN DEGREE AND OF REFLECTING THE SAME WHEN IONIZED TO A THE GIVEN DEGREE, IONIZING ELECTRODE MEANS IN SAID WAVEGUIDE MEANS, SAID ELECTRODE MEANS EXTENDING ALONG A GIVEN LENGTH OF SAID WAVEGUIDE MEANS AND PROTRUDING FROM A SHORTER SIDE THEREOF A GIVEN DISTANCE, AND ENERGIZING MEANS CONNECTED TO SAID ELECTRODE MEANS FOR CAUSING THE SAME TO IONIZE THAT PORTION OF SAID FLUID OCCUPYING THE SPACE IN SAID WAVEGUIDE MEANS BETWEEN SAID ELECTRODE MEANS AND SAID LONGER SIDES TO THE GIVEN DEGREE, SUCH IONIZATION OF SAID FLUID THEREBY SERVING TO EFFECTIVELY REDUCE THE SIZE OF SAID WAVEGUIDE MEANS, WHEREBY THE PHASE OF MICROWAVES IN SAID WAVEGUIDE MEANS IN CORRESPONDINGLY CHANGED. 